In "The Gift of the Magi" by O. Henry, what is an example of foreshadowing?

When "The Gift of the Magi" by O. Henry begins, we find Della crying because she does not have enough money to buy her husband Jim a Christmas present. That might lead us to predict that he will not get a gift, but shortly after, Della sees herself in the pier glass, and we see an idea being formed. She lets down her beautiful long hair, looks at herself, pins her hair back up, grabs her coat, and hurries out.

"Suddenly she whirled from the window and stood before the glass. Her eyes were shining brilliantly, but her face had lost its color within twenty seconds. Rapidly she pulled down her hair and let it fall its full length." (Henry 2)

We then find out that Della's hair was something in which the couple took great pride-her hair and Jim's pocket watch were their two most valuable possessions. It only follows that because of their deep love for one another, they will give up anything in order to give the other a special Christmas gift. Of course O. Henry is a master, and we don't see it coming until it has already happened!

"So now Della's beautiful hair fell about her rippling and shining like a cascade of brown waters. It reached below her knee and made itself almost a garment for her. And then she did it up again nervously and quickly. Once she faltered for a minute and stood still while a tear or two splashed on the worn carpet."